1. Field of the Invention
The present invention is related to a structure of digital transmission line, and especially to such a structure having the characteristic impedance thereof maintained at 75xcexa9, when in transmission, no refraction or reflection of signal is induced; the digital transmission line particularly suits signal transmission.
2. Description of the Prior Art
Conventional structures of signal transmission lines, such as the coaxial cable structure shown in FIG. 1, are characterized in that: the insulation portion enveloping a conductor 1 is made a cylinder member 2 formed as a coaxial cable by press shaping of PE, and is combined with a Mylar tape 3 made from aluminum foil, an obscuring layer 4 made by knitting copper lines and a PVC enveloping member 5.
The coaxial cable is a round PE pipe made by press shaping, in order to lower its electric capacity and attenuation rate. However, the effect of insulation of PE is not the best, and the obscuring layer is not able to make 100% obscuring, and it is still a problem to be solved that it is not certain whether the characteristic impedance can be maintained under 75xcexa9, what will be the degree of mutual interference among a magnetic field, radio frequencies and static electricity, and whether refraction or reflection of transmitted signals is induced during transmission.
Thereby, it is the motive of the present invention to improve on the conventional structure of coaxial cables with the above stated defects, and to provide a structure of digital transmission line able to make 100% obscuring, to minimize the degree of mutual interference among a magnetic field, radio frequencies and stationary electricity, to maintain the characteristic impedance at 75xcexa9 and to assure no refraction or reflection of transmitted signals is induced during transmission.
The primary object of the present invention is to provide a structure of digital transmission line of which the characteristic impedance can be maintained at 75xcexa9.
The secondary object of the present invention is to provide a structure of digital transmission line with which the degree of mutual interference can be minimized, and 100% obscuring can be obtained.
Another object of the present invention is to provide a structure of digital transmission line with which no refraction or reflection of transmitted signals is induced during transmission.
To achieve the above stated objects, the present invention is comprised of a core material, a middle material layer and a coating layer; the core material is a transmission medium enveloped with an insulation polyethylene (PE) foam layer; the coating layer includes at least one layer and is made of polyvinyl chloride (PVC), the middle material layer is provided between the core material and the coating layer, and is characterized by that the middle material layer is comprised of a copper foil wrapping layer, at least a metallic-wire knitting layer and a foamed Teflon-tape wrapping layer (polytetrafluoroethylene, PTFE). The middle material layer can get 100% obscuring, can minimize the degree of mutual interference, can maintain the characteristic impedance at 75xcexa9, and can get the result that no refraction or reflection of transmitted signals is induced during transmission.